The present invention is directed to an apparatus and method for manufacturing articles made of polyurethane. More specifically, the invention is directed to an apparatus having a mix chamber positioned below and in direct communication with a mold assembly.
Polyurethane foam has been used for many years for cushioning, insulation and other applications. Polyurethane foam is usually manufactured at atmospheric pressure from polyester or polyether based polyols combined with isocyanates, such as toluenediisocyanate (TDI), polymethylene polyphenylisocyanate (MDI), or mixtures thereof, and additives to form a finished product ranging from a very flexible to a very rigid product. The cell structure of the foam can range from completely open to completely closed. Examples of open cell, flexible polyurethane foam technology are disclosed in U.S. Pat. No. 4,451,583.
Expanded flexible polyurethane articles can be manufactured by the continuous conveyor method or by the molding method. Most expanded flexible polyurethane is currently produced by the continuous conveyor method for producing slabs or by molding articles in a noncontinuous process. The continuous conveyer method or "slab-stock" method is used to process the majority, by weight, of flexible polyurethane foam. In this method, the liquid chemicals are mixed together and poured on a carrier sheet of plastic or paper. The carrier sheet rests either on a conveyor flat floor with two vertical sides or on a conveyor with a round shape. As the chemicals proceed down the conveyor, they rise or expand in the form of closed cells. In the case of open cell foam, as the reacting chemicals reach full expansion, the cell walls open and flow into struts. These struts continue to solidify until an almost cured dry article is formed. At the end of the conveyor, a saw cuts off a length of the article. The article is then taken to a storage area for final curing, which usually takes about 24 hours. This process is continuous until the machine is stopped.
In the alternative molding method, the liquid chemicals are mixed and deposited in a mold, with or without a lid, and the chemicals expand to the shape of the mold. It is important that the chemicals in a mold be mixed in a short interval of time so that the chemicals react properly. One common prior art molding method for large parts is known as the "bucket method". In the bucket method, a mix chamber for mixing the liquid chemicals is located above the interior of a separate mold. The chamber is removed after the mixed chemicals are released in the mold. The chemicals expand and an article is formed in the mold. The bucket method has the disadvantage of being relatively complicated, difficult to clean, and produces foam full of blow holes. Further, the mix chamber in the bucket method is not in direct communication with the mold.
The present invention overcomes the disadvantages of the bucket method while retaining the major bucket method advantage of mixing the chemicals all at once. The mix chamber in the present invention is in direct communication with the mold. The present invention can be used alone to produce polyurethane articles with or without auxiliary blowing agents. It can also be used in a vacuum chamber to eliminate blowing agents as disclosed in my U.S. Pat. No. 5,182,313, the teachings of which are incorporated herein by reference, or a positive pressure chamber depending on the application.